Capacitive fill-level measuring devices are known in the state of the art. The measuring principle is based on having a measuring probe and a second probe, or the wall of the container in which the medium is located, form the two electrodes of a capacitor, with the medium as dielectric. The capacitance of the capacitor depends on the fill level of the medium and permits, consequently, the determining of fill level. For the measurement, the probe is usually supplied with a drive signal, which is an electrical alternating voltage of predeterminable frequency. The response signal is usually an electrical current signal, which is, most often, converted to an alternating voltage. From the response signal, then the fill level is determined.
A problem with this arrangement involves the fact that the medium can form an accretion on the probe, and the accretion then influences the measurement negatively. Especially, very viscous material tends to cling to the probe unit and thus form an accretion. Accretion can, in given circumstances, lead to the fact that a fill level measurement is no longer possible, because the accretion acts as if it were a metallic isolation around the probe.
Thus, an object of the invention is to provide a capacitive measuring apparatus, with which, even in the case of media tending to accrete, the fill level can be determined as reliably as possible.